Anti-bow bar assembly for filter belt



Feb. 13, 1968 W. H. SANDERSON ANTI-Bow BAR ASSEMBLY FOR FILTER BELT Filed NOV. 22, 1965 2 Sheets-Sheet l INVENTOR ML 75K/6( SAA/@EPSON ATTORNEYS Feb. 13, 1968 w. H. SANDERSON ANTI-BOW BAR ASSEMBLY FOR FILTER BELT rm mm F me @H mmmmmimmmm@Mummmmwmmmmmm@,- smm\\ L f @H oww om INVENTOR,

Wurf/Q 54N@ E/ZSON 510.73m, M, ua/5M ATTRNEYs United States Patent O 3,368,685 ANTI-BOW BAR ASSEMBLY FR FILTER BELT Walter H. Sanderson, Greenbroolr, NJ., assigner to Komline-Sanderson Engineering Corporation, Peapack, NJ., a corporation of New .lersey Filed Nov. 22, 1965, Ser. No. 509,025 12 Claims. (Cl. 21d-401) ABSTRACT F THE DTSCLSURE An apparatus having plural series of rollers adjustable with respect to each other to act against adjacent sections of a lilter web to correct for leading or trailing bows in the same. The middle series of rollers is supported on a main frame with the outer two series on adjustable auxiliary frames carried by said main frame; the individual rollers being carried at varying distances from the longitudinal axis of the frame for the desired web support and skewed to stretch the web. Tapered end rollers are included to guide the reinforced edge of the web.

This invention relates to improvements in attachments for continuous filter units which employ a moving filter web or -belt and, more particularly, to an anti-bow bar assembly for guiding the resiliently stretchable web to counteract relative displacement of portions of the web in the direction of the web movement.

It has been recognized that transverse displacement of the stretchable belt type filter in a rotary vacuum filter unit is, at least, partially traceable in its inception to one portion of the web moving faster than an adjacent portion. This condition causes tracking problems of the web on the filter rolls and wrinkling of the web that might eventually result in tearing or separation of the filter web from the edge guides and thus costly shutdowns of the lter unit during repairs.

This problem is sometimes related to the edges of the filter web in that in some instances one edge of the web will tend to run ahead of the other edge thus deformlng the web and creating Wrinkles and the tearing of the filter web from the edge guides as mentioned. This problem has been sufficiently solved by the filter belt regulating means and process disclosed in the U.S. patent to Komline et al., 3,090,488, granted May 2l, 1963, and assigned to the present assigner, by maintaining normally transversely aligned points in the web in the proper position by use of an expandable discharge roll or the like operated by sensing means positioned at opposite side edges of the web. The underlying concept of this patent then is to vary the relative length of the endless circuitstranversed by the adjacent portions of the filter web and, thus, by changing the times required for completion of the respective circuits by increasing or decreasing their lengths, the web is advantageously maintained in alignment in the transverse direction.

The present invention relates to the additional but related problem caused by the tendency of the upper run of the filter web or belt as it leaves the vacuum roll to bow about the central axis due to the weight of the filter cake or, in other cases, due to the action of the helical discharge roll on the web in the Flexibelt type filter' unit, such as is shown in the U.S. patent to Hawkes et al., 3,017,997, granted Jan. 23, 1962, and assigned to the assignee of the present case. This additional displacement ot' portions of the filter web in the transverse direction that normally occurs on the upper run of the filter web, that is, between the relatively large diameter filter drum or roll and the discharge roll can be of such a nature as to cause the Web to exhibit either a leading bow if the middle of 3,368,685 Patented Feb. 13, 1968 the web is running ahead of the edges of the web or a trailing bow if the edges of the web happen to be running ahead of the middle of the web. It will be recognized that if such a bowing of the web is permitted to continue then the aforementioned tracking problems will arise thereby resulting in the inherent reduction in efficiency of the filter followed by the premature failure of the filter web and shutdown of the filter unit.

In accordance with the present invention, it is proposed to provide an improved anti-bow bai assembly for guiding this flexible and stretchable filter web along the upper run of said web that adopts the principles of the aforementioned Komline et al. patent of regulating the length of the feed path of the adjacent portions of the filter web between the filter drum and the discharge roll. This is accomplished in an advantageous manner by means of a plurality of series of rollers that act against the adjacent width sections of the web with adjusted pressure so as t0 increase or decrease the length of travel along the upper run of the belt as desired. According to the preferred embodiment illustrated, the series of rollers acting on the middle section of the web is mounted on an elongated main frame that extends across the filter web and is journaled for rotation by the side plates of the filter unit. The rollers that are adapted to engage the right and left side portions of the web adjacent the edges of said web are carried by auxiliary frames that are journaled for rotation on the main frame whereby adjustment between the several series of rollers may be provided in accordance with the type of bow that is detected in the filter web.

As will be apparent upon consideration of the detailed consideration of the description that follows, when the rollers of any section are pressed against the adjacent portion of the lter web then that portion of the web will have an increased feed path length between the filter roll and the discharge roll so that in effect that portion of the web is slowed down to allow the other portions to catch up and bring the belt into normal transverse alignment. Thus, if a leading bow is detected in the web, that is if the center of the web is moving ahead of the side portions of the web, then the rollers positioned along the center of the web are brought into pressure engagement so as to increase the feed path of that portion of the web and thus allow the edge portions to catch up. Conversely, if a trailing bow is detected, that is if the center of the web is trailing behind the side portions, then the outside rollers are brought into pressure engagement while the rollers along the center portion of the web are merely held into touch contact with the web which thereby causes a slowing down of the side portion of the web adjacent the edges toallow the center portion of the web to resume transverse alignment with the edges.

The elongated main frame of the anti-bow bar assembly in the preferred embodiment disclosed herein for purposes of illustration of the invention comprises an elongated bar that forms the longitudinal pivot axis of said frame and a series of radially extending pairs of supports of progressively decreasing lengths on both sides of the roller positioned along the center line of the web so that the guiding action caused by the rollers mounted on the supports is progressively decreased from the center line of the web to the outer limits of the center portion of the web engaged by these rollers. On each end of the bar there are provided concentric sleeves having radially extending pairs of supports for the rollers that engage the side portions of the web, and these pairs of supports are progressively increased toward the outer edge limits of the web so that the length of the path traveled by the outer limits of the web is progressively increased toward the outer edges of said web. This configuration thus desirably results in the feed path being varied within each of the independent width portions of the web so as to counteract the relative displacement or bowing of the web within said width portions.

The bar assembly of the invention is mounted by side plates of the filter unit such that the radially extending supports are preferably positioned substantially parallel to the upper run of the filter web. With this arrangement, the rollers press against the web with substantial leverage when they are adjusted into Contact with said web giving the desired regulating or guiding action. There are provided simple `adjustment means that are easy to manipulate between each end of the main frame and the side plates and between the main frame and the auxiliary frame to accomplish the independent regulation between the adjacent portions of the web las described.

For the purpose of preventing undue stresses being placed on the adjusted web along the upper run that might weaken the web or cause premature breaking up of the filter cake, the adjacent rollers of the plural series of rollers are supported substantially t-he same distance from the longitudinal pivot axis of the main frame of the assembly so as to give the required transition zone between the adjacent portions of the web. In addition, as will be apparent to those skilled in this art, there is no appreciable surface wear on the filter web since the freely rotating rollers frictionally rub the belt only a minimum amount.

Another feature of the apparatus of the present invention involves the skewing of the rollers that are in operative engagement with the right and left side portions of the web so as to maintain said web in substantially wrinkle-free condition and to resist the tendency of the outermost edges of the belt to be pulled inwardly due to the deformation caused by the pressure engagement of the rollers with the web. Further, the outermost roller of each of the series of rollers that act on the outer portions of the web are frusto-conical in shape with an outwardly tapered surface terminating in an upstanding flange that serves to conveniently position the usual reinforced edge ot the filter web.

The apparatus is simple in construction such that it is inexpensive to manufacture and the parts are easily replaced if needed. Further, this anti-bow bar assembly can be placed in service on existing filter units without any modification of the operative parts of the machine and therefore with a minimum amount of expense. As a result, the assembly can be used in a variety of types of filter web units with success as long as the web employed is substantially resiliently stretchable so as to deform in response to the relative `adjustment of any number of plural series of rollers used.

The resiliently stretchable filter web is of the usual construction in that it can be made of a porous web of rubber or other resilient material or, in the alternative, can be of composite construction wherein a stretchable filter cloth web has a pair of elastic bands secured to the opposite side edges to impart elasticity thereto. As is well known in the art, such elastic edges serve to reinforce the filter web belt as well as serving in cooperation with the outer rollers to prevent axial displacement of the belt as previously mentioned.

Thus, it is one object of the present invention to provide an improved anti-bow bar assembly for `a resiliently stretchable filter web.

It is another object of the present invention to provide an anti-bow bar that is simple in construction and easily adjustable to counteract relative displacement of `adjacent portions of the web in the direction of the web movement.

It is still a further object of the present invention to provide an anti-bow bar assembly that comprises a main frame and auxiliary frame, both of said frames having separate roller guiding surfaces for engaging different portions of the filter web with adjustment means for independently adjusting the auxiliary frame with respect to the main frame to vary the guiding relationship between the surfaces independently of each other.

It is another object of the present invention to provide an anti-bow bar assembly of the type described that causes a minimum amount of drag and wear on the surface of the filter web and a minimum amount of undesirable distortion of t-he web.

it is still a further object of the present invention to provide an anti-bow bar assembly for a filter web that can be easily and quickly adjusted to compensate for either a leading or trailing bow condition in the filter web by a simple adjustment without the need for replacement of parts.

It is another object of the present invention to provide an anti-bow bar assembly with spaced parallel rollers that are positioned such that relative displacement of the filter web within a predetermined width portion is automatically counteracted.

It is an additional object of the present invention to provide an anti-bow bar assembly having the guiding sur faces adjacent the edges of the web skewed outwardly to maintain the web in substantially wrinkle-free condition and to discourage an inward creeping of the edges of the web due to deformation of the web by the device.

It is still another object of the present invention to provide an anti-bow bar assembly of the type described wherein the adjacent rollers of the several series of rollers of the bar assembly are substantially in the same guiding plane in any normal adjusted position so that the transition zone from one section to another is provided.

Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustnation of the best mode contemplated by me of carrying out my invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description lare to be regarded as illustrative in nature, and not as restrictive.

Referring now to the drawings:

FIGURE 1 is a partial side elevational view of a filter unit of the type described with the apparatus of the present invention applied thereto;

FIG. 2 is a rear view in elevation of the device of the present invention, that is, a view of the device looking in the direction opposite to the travel of the filter web;

FIG. 3 is a bottom plan view of the device of FIG. 2;

FIG. 4 is a cross-sectional view taken along lines 4--4 of FIG. 3;

FIG. 5 is an enlarged detailed view in side elevation of that portion of FIG. 1 showing the device of the present invention;

FIG. 6a is a schematic illustration of the effect of the device of the present invention on a filter web ex- Ihibiting la leading bow; and

FIG. 6b is a similar schematic illustration of the effect of the device of the present invention on a trailing bow in said web.

With reference to FIGURE 1 of the accompanying drawings for a more specific description of the invention, there is shown a partial view of a vacuum-filter unit, generally designated by the reference numeral 10, which filter unit 10 comprises a suitable rigid frame 11 for supporting a conventional large diameter vacuum drum or roll 12 that has a porous stretchable web 13 disposed about the outer peripheral sunface in the usual manner. The drum 12 is normally driven about its axis in such a manner that the web 13 is moved through the liquid contents of a tank (not shown) and due to the vacuum within the drum 12 a liquid filtrate is forced through the pores of the web 13 leaving a filter cake on the surface of the web 13.

There is provided a discharge roll 15 about which the web 13 is guided in the normal manner to cause a breaking up of the -filter cake for delivery of the same to la suitable receiver (not shown). After the web 13 has passed around the discharge roll 15, which may have a helix surface to encourage breaking up of the cake as shown in the aforementioned Hawkes et al. patent, the Web 13 continues past la spray pipe 16 for cleaning and then up and over a return roll 17 and back onto the surface of the drum 12 thus completing the endless circuit of the web 13.

In the filter unit illustrated merely for the purpose of disclosing the invention, the discharge roll and the return roll 17 are conveniently journalled for rotation by :a pair of side plates 20, 21 (FIGS. 1 and 6a) that are suitably positioned on the supporting frame 11 at each end of the vacuum roll 12. Since this general organization of elements is conventional and operates in the usual manner, further discussion of these parts and their operation is deemed to be unnecessary for an understanding of the device of the present invention.

Also mounted between the side plates 20, 21 is an antibow bar assembly, generally designated by the reference numeral 25 and constructed in accordance with the present invention. As well illustrated in FIG. 1, the bow bar assembly 25 lies adjacent the upper run of the filter web 13 between points designated x and y for identification so that said assembly 25 is in a position to engage said web 13 between the vacuum roll 12 and the discharge roll 15.

As best shown in FIGS. 2 and 3, the anti-bow bar assembly 25 comprises a main frame 26 that consists of an elongated bar or rod 27 that extends the entire distance between the side plates Ztl, 21 and a plurality olf pairs of radially extending roller supports 2S spaced along the central portion of the bow bar assembly 25. The ends of the rod 27 are suitably journalled in the side plates 20, 21 so that said bow bar assembly 25 is capable of pivotal adjustment toward and away from said web 13, which will be explained below.

Each of the pairs of the radially extending supports 28 carry a suitable individual roller 29, each of which is journalled for rotation about ,a separate parallel axis in a progressively decreasing manner on both sides of the center roller due to the difference in length of the pairs of supports 28, -as shown in FIG. 3. The rollers 29 thus `combine to form a center roller series, collectively identified by the reference numeral 30, which is in an overall shape of an upside-down V. An auxiliary frame is provided in a right and left section 33a, 33h, respectively, iat opposite ends of the rod 27 and each frame section 33a, 3311 takes the form of a sleeve 34 having a plurality of pairs of radially extending supports 35. A pair of side roller series 36a, 36b is formed by similar individual rollers 37 that are carried by the pairs of supports 35. The right and left series of rollers 36a, 36b thus formed are adapted for engagement with the respective side portions of the web 13. The paired supports 35 are orf progressively increasing length toward the ends of the 'bar assembly 25 thus presenting said series of rollers 36a, 36b diagonally across the assembly 25 to form the outer legs of a W-shaped configuration; the inside legs being formed by the V-shaped roller series 3G, the latter of which thus occupies the space between said roller series 36a, 36b (see FIG. 3).

As shown in FIGS. 2 and 3, the paired supports 35 are turned so as to present the rollers 36 in an outwardly skewed condition for the purpose of constantly urging the web 13 toward the outer limits of the guide 'oar assembly 25 to create in the filter web 13 a smoothing effect on the side portions of said web 13 to prevent wrinkling and dislocation of the web 13 due to the action of the bow bar assembly 25. For the purpose of aiding in the guiding of the web 13, the outermost roller of the right and left series of rollers 36a, 35h is truste-conical in shape having an outwardly tapered surface 38 that terminates in an upstanding flange 39 that serves to limit the axial movement of the edges of the web 13. The axis of the frustoconical roller in said series 36a, 36b is not skewed in the manner of the individual rollers 37 so that the edge of the web is given a straight feed path past the bar assembly 25 and presented to the discharge roll 15 (FIG. l) in the proper manner.

In order to adjust the auxiliary frame sections 33a, 3-3b with respect to the main frame 26 so as to -be able to vary the relative degree of guiding action afforded by the center roller series 3i) with respect to the right and left roller series 36a, 36b, the sleeve 34 is provided with a slot 4t? (FIGS. 2 4) through which a suitable adjusting screw 41 passes into threaded engagement with the bar member 27. Thus, when it is desired to adjust the angular relationship of the first mentioned roller series 30- with respect to the second mentioned roller series 36a, 36b to vary the relative guiding relationship of the rollers with the web 13, the screw 41 is loosened whereupon the sleeve 34 can 'be easily adjusted with respect to the rod 27; then, after the desired relationship has 4been obtained, the screw 41 can be tightened into engagement with the sleeve 34, whereupon said roller series 30 is securely locked in the desired relationship with respect to the side roller series 35a, 3d!) being adjusted.

The over-all adjustment of the anti-bow bar assembly 25 can be effected by structure best shown in FIG. 5 of the drawings and now to be described. That is, a lever 45 is fixed to each end of the bar member 2'7 by an integral collar 46. It can be seen that upon rotation of the lever 45, the bar member 27 is rotated so as to adjust the pressure of the rollers against the web 13 to cause an outward adjustment of the feed path in the manner indicated in this figure. This adjustment is effected by any simple means such as a jack-screw 48 that is pivoted to the end of the lever t5 and engages the stationary flange 49 fixed to the side plates 29, 21. This jack-screw 48 is locked or secured in a desired position by a pair of lock nuts 50, 51 which thereby fix the over-all roller pressure adjustment.

As viewed in FIG. 5 when the bar assembly 25 is in pressure engagement with the web 13, said web y113 is given a slight outward bulge at the point of engagement with the individual rollers 31 or 37 as the case may be, as indicated by the reference numeral 55. It is this outward bulge 55 that is operative to increase the length of the feed path between the point x where the upper run of the filter web 13 leaves the filter roll 12 and the point y where the filter web engages the discharge roll 15 (see FIG. l).

In other words, during the operation of the filter system 1G, if it is desired to increase the feed path of the upper run of the filter web 13 then the pressure of the individual rollers 31, 37 against the appropriate section of the web 13 is increased. This is done by first properly setting the angular relationship between the main frame 26 and the auxiliary frame sections 33a, 33b by operating the lock screw 41 and, secondly, by operating the jack-screw 48 so as to rotate the bar assembly 25 in the counter-clockwise direction indicated by the solid arrow in FIG. 5 whereupon the outward bulge 55 is increased and the distance between the points x and y on the filter belt 13 is accordingly increased.

In the preferred embodiment illustrated, the support arms 2S, 35 extend substantially parallel to the upper run or", the web 13, as shown in FIG. 5, so that the individual rollers 31, 37 can in at least one adjusted position be in engagement with the web 13 only to the extent as to operatively touch said web in supporting relationship without causing outward bulging of the web 13. In other words, if the adjustment nuts 5t), 51 are positioned on the jack-screw 48 so that the rollers 31, 37 do not engage the web 13 under pressure then there is no outward bulge at 55 and the feed paths between x and y remain unchanged.

It will be remembered that the problem solved by the apparatus of the present invention is the longitudinal bowing of the upper run of the lter belt 13 as `the result of the formation of the filter cake on the web and/ or due to the stretching action on the edges of the web 13 by the discharge roll 15, The rst condition that might appear is schematically shown in FG. 6a wherein the web 13 upstream of the bow bar assembly 25 of the present invention exhibits a leading bow condition; this being schematically illustrated by a series of bowed lines 60. When this condition is present and detected, the center series of rollers 3@ is brought into pressure engagement with the center of the filter web 13 and the side series of rollers 36 are adjusted so as just to touch the underside of the web in supporting relationship without exerting notable pressure thereon. This adjustment is made by 4loosening the set screw 41 and rotating the sleeve 34 upon the rod 27 until the auxiliary frame sections 33a, 33h are positioned at the desired negative angle to the main frame 26. After this has been done, it can be seen that the center series of rollers 30 is pressing against the underside of the filter `web 13 so as to cause an outward bulge 5S (FlG. 5) whereas the right and left roller series 35a, 36b are such as to be drivingly engaged by the web 13 but do not form the outward bulge 55 along the right and left sides of the web 13. As the result, the feed path between the points x and y of the web 13 is lengthened along the center portion thereof while the feed path along the right and left sides is virtually unaffected,

Once the feed path of the center portion of the web 13 has been increased it will take a longer time for it to traverse the distance x, y than is the case in the right and left side portions of the web so that as a result said center portion (engaged by the roller series 3d) is retarded to allow the side sections of the web 13 (engaged by the right and left roller series 35a, 36h) to catch up as schematically shown by straight transverse lines 61 on the downstream side of the anti-bow bar assembly 25 in this ligure.

Conversely, if it is desired to correct for a trailing bow, that is where the center portion of the belt trails the side edges, then the auxiliary frame sections 33a, 33]; are adjusted to a positive angle with respect to the main frame 26 that supports the same, so that upon adjusting the bar assembly 25 by the use of the jack-screw 48 and lock nuts Se, 51, the side portions of the web 13 are engaged by the right and left roller series 36a, 36h, under pressure, whereas the center roller series 3d is positioned so as to just touch in supporting relationship the center portion of said web 13. In this case, the feed path of the side portions of the web 13 will be increased between the points x, y wit-h a resultant slowing down of these portions of the web whereupon the normal condition represented by the straight transverse line 61 is once again assumed.

As will be realized from viewing FlG. 6a, the greatest amount of guiding action to counteract the leading bow 60 must be presented to the center of the web since the apex of the bow is at this point. To accomplish this, the support arms 2S for the middle roller 29 of the center roller series 30 are longer than the pair of roller support arms 28 for the adjacent roller 29; and the support arms 28 for each succeeding roller 29 in the center series 30 are progressively reduced. Thus, when the rollers 29 are brought into engagement with the web 3i), due to the difference in the lever arm (support arms 2S) that presents the rollers to the surface of the web 13, the feed path within the center portion of the belt will be the greatest at the center of the belt where the need for correction is the greatest and will be progressively decreased toward the outer limit of the center section of said belt 13 where the need is less.

Likewise, since the support arms 35 for each of the roller segments 37 are progressively increasing in length from the inner ends of the sleeves 34 to the outer end of said sleeves 34 there is progressively increasing guiding action provided toward the edges of said web 13. This is done since the greatest counter action applied to the trailing bow must be made at the edges of the web to provide for the most efficient recovery, as can be seen in FIG. 6b of the drawing.

As explained above, since the frusto-conical surface 38 of the outermost roller in the side roller series 36a, 35h is tapered outwardly and terminates in the upstanding ange 39, the edge of the web is desirably retained in a straight line across the bow bar assembly 25. For eX- arnple, if one edge of the web tends to ride to the center of the bow bar assembly 25, then the outwardly tapered surface of the roller 38 will serve to urge that edge back against the limiting flange 39 Vwhereupon normal tracking of the web is achieved.

In addition to the centering feature of the frusto-conical roller surface 38 as it interacts with the edge of the web 13, it will be remembered that the remaining rollers 37 of the side rollers series 36a, 3tib are positioned at a small angle with res-peet to the horizontal so as to urge the side portions of the web 13 constantly outward to eliminate the tendency of said web 13 to wrinkle and to counteract the inherent inward pulling action caused by the outward bulge at 5S caused by pressure engagement of the selected series of rollers 30 or 36a, 366. Further, since the only portion of the bow bar assembly 25 that touches the web 13 is the rollers 29, 37, then the wear on said web 13 is reduced to a minimum. Also, since there is continuity in the line of the several rollers 29, 3'7 forming the W-conguration, that is, since there is no abrupt difference in the positioning of the rollers but rather a progressive one, then the possibility of undue stretching of the `web that, for example, hight result in premature breaking up of the filter cake is minimized.

From the foregoing, it will be realized that the antibow bar assembly 25 constructed in accordance with the lpresent invention has certain other results and advantages that have heretofore not been attainable in this art; namely, the adjustment of the bow bar that can regulate the relative position of portions of the web along the direction of web travel can be obtained rapidly with a very simple adjustment without the necessity of rutilizing the complicated structures and methods of the prior art. Further, the apparatus is inexpensive to manufacture and the parts are so related so as to be easily replaced if needed. Further, in tests it has been found that this apparatus once set to the particular operating conditions of the machine will keep the belt or web 13 in alignment without difficulty and maintain the said belt 13 in a substantially wrinkle-free condition for an extended period.

in this disclosure, there is shown and described only the preferred embodiment of the invention, but, as aforementioned, it is to be understood that the invention is capable of various changes or modifications within the scope of the inventive concept as expressed by the accompanying claims.

What is claimed is:

1. In a continuous belt-type lter unit, an anti-bow bar assembly for guiding a resiliently stretchable lter web disposed along a feed path between a pair of spaced parallel rolls to counteract relative displacement of portions of said web in the direction of the web movement comprising an elongated main frame extending across said web, means for mounting the ends of said main frame to provide for adjustment of the same, first roller means rotatably mounted on said main frame, an auxiliary frame carried .by said main frame, second roller means rotatably mounted on said auxiliary frame and spaced from the central axis of said main frame, said rst and second roller means being adapted to be drivingly engaged by respective `first and second width portions of said web so that said roller means guide said web, and

means to adjust said auxiliary frame with respect to said main frame to vary the guiding relationship of said Second lroller means independently of said rst roller means, whereby the relative degree of guiding action `aiorded by said irst and second roller means can be adjusted to independently vary the length of said feed path between said rolls that is traversed by said portions of said web to allow for correction of either leading or trailing bow in said web.

2. The combination of claim 1 wherein said first and second roller means comprise a first and second series of spaced-apart rollers, respectively, said rollers being of equal diameter and mounted on the respective frames by individual parallel shafts, the distance between said parallel shafts being such that the length of said feed path at -a given point across the respective width portions of said web varies so as to counteract said relative displacement of said web within that width portion.

3. In a continuous belt-type lter unit, an anti-bow bar assembly for guiding a resiliently stretchable filter web disposed between a pair of spaced parallel rolls to counteract relative displacement of portions of said web in the direction of the web movement comprising an elongated main frame extending across said web, means for mounting the ends of said main 'frame to provide for pivotal adjustment of the same and for fixing the same against pivotal movement during the guiding operation, lirst roller means rotatably mounted of said main frame, an elongated auxiliary frame pivotally carried by said main frame and spaced from the central axis of said main frame, second roller means rotatably mounted on saidv auxilary frame, the longitudinal pivot axes of both said main frame and said auxilary frame extending substantially transverse to the direction of movement of said web and substantially parallel to the plane of the web, said rst and second roller means mounted opposite their respective pivot axis for movement toward and away from said web, said rst and Second roller means being adapted to be drivingly engaged by respective rst and second width portions of said web so that said roller means support and guide said Web, and means to adjust the angular relationship between said main frame and said auxiliary frame, whereby the relative degree of guiding action afforded by said rst and second roller means can be adjusted to vary the length of the path between said rolls that is traversed by at least one of said portions of said web to allow for correction of either leading or trailing bow.

4. The combination of claim 3 wherein said lirst and second roller means comprise a rst and second series of spaced-apart rollers, respectively.

5. The combination of claim 4 wherein said iirst portion of said web is centered along the longitudinal center line of said web and said main frame comprises a bar of circular cross section, a plurality of radially extending supports on said bar for mounting said rst series of rollers, said supports being of progressively decreasing length on both sides of the roller positioned along the center line of said web whereby progressively decreased guiding action may be provided toward the outer limits of said first portion so that the length of the path traversed by said rst portion is accordingly progressively decreased from said center line to said outer limits.

6. The combination of claim 5 wherein the second portion of said web extends along both sides of said web between the outer limits of said rst portion and the outer edges of said web and said -auxiliary frame comprises a pair of cylindrical sleeves surrounding said bar opposite said second portion of said web, a plurality of radially extending supports on said sleeves for mounting said second series of rollers, said supports being of progressively increasing length from the inner ends of said sleeves to the outer ends whereby progressively increased guiding action may be provided toward the edges of said web so that the length of the path traversed by said second portion is accordingly progressively increased toward the outer edges of said web.

7. The combination of claim 6 wherein the two outermost rollers of said second series of rollers are frustoconical with an outwardly tapered surface terminating in an upstanding flange to accommodate the outer edges of said web to facilitate self-centering action of said web.

8. The combination of claim 7 wherein the remaining rollers of said second series are skewed outwardly through a small angle to prevent wrinkling of said web.

A9. The combination of claim 6 wherein the adjacent supports of said rst and second series of rollers are substantially the same length to provide a transition zone in said web between said rst and second portions.

10. The combination of claim 6 wherein said supports are normally extended substantially parallel to said web.

11. In a continuous belt-type lter unit, an anti-bow bar assembly for guiding a resiliently stretchable filter Web disposed along a feed path between a pair of spaced parallel rolls to counteract relative `displacement of portions of said web in the direction of the web movement comprising an elongated frame extending across said web, W-shaped guiding means mounted on said frame, said guiding means being divided into a par of inside legs forming an inverted V-shaped middle section and a pair of outside legs forming an outer leg section, said middle section extending generally in the direction of said web movement, said middle and outer sections being adapted to be engaged by the middle and the outer portions of said web respectively to guide said web, means to independently adjust the pressure relationship of said middle section and the outer leg section of said guiding means against said web, whereby the relative degree of guiding action afforded by said rst and second roller means can be adjusted `to independently vary by incrementally increasing or decreasing the length of s-aid feed path between said rolls that is traversed by both said middle and outer portions of said web to allow for correction of either leading or trailing bow in said web.

12. The combination of claim 11 wherein said guiding means includes plural series of rollers journaled for rotation about each of said pairs of inside and outside legs, and said outer section of said guiding means is mounted on an auxiliary frame carried by said main frame.

References Cited UNITED STATES PATENTS 3,090,488 5/1963 Komline et al. 210-401 X 3,120,492 2/ 1964 Peterson 210-401 3,227,281 1/ 1966 Peterson et a1. 2.10-401 X `3,262,576 7/1966 Davis 210-401 FOREIGN PATENTS 207,240 3/ 1957 Australia.

REUBEN FRIEDMAN, Primary Examiner.

J. ADEE, Assistant Examiner. 

